Roane County climate

Roane County Frost Dates and Growing Season

NOAA 1991-2020 normals for Spencer, 9.7 km from Roane County, elevation 972 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Spencer. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around April 30 and the first fall freeze around October 17, a growing season of about 169 days.

Median at 36°F
last May 9, first October 6
Median at 32°F
last April 30, first October 17
Median at 28°F
last April 19, first October 27

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 28May 21May 17May 13May 9May 6May 3Apr 29Apr 24
32°FMay 18May 11May 7May 3Apr 30Apr 26Apr 23Apr 20Apr 15
28°FMay 8May 1Apr 26Apr 22Apr 19Apr 16Apr 13Apr 7Apr 1
24°FApr 22Apr 17Apr 13Apr 8Apr 5Apr 2Mar 30Mar 25Mar 20
20°FApr 11Apr 4Mar 31Mar 29Mar 24Mar 21Mar 17Mar 12Mar 4
16°FApr 1Mar 26Mar 20Mar 16Mar 13Mar 8Mar 3Feb 28Feb 20

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 23Sep 28Oct 1Oct 3Oct 6Oct 8Oct 11Oct 14Oct 19
32°FOct 3Oct 7Oct 11Oct 14Oct 17Oct 19Oct 22Oct 26Oct 29
28°FOct 13Oct 18Oct 21Oct 24Oct 27Oct 30Nov 1Nov 4Nov 9
24°FOct 24Oct 29Nov 1Nov 4Nov 6Nov 9Nov 13Nov 16Nov 23
20°FNov 3Nov 8Nov 11Nov 15Nov 18Nov 22Nov 27Dec 1Dec 7
16°FNov 11Nov 17Nov 23Nov 29Dec 2Dec 6Dec 12Dec 18Dec 27

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F168162158153149145140135127
32°F188181176172169165160154146
28°F212205199194191186182176168
24°F240230223219215211206200194
20°F268258252246240235228221214
16°F299288279272266261255247237

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
5,338
Cooling degree days, base 65°F
749
Growing degree days, base 40°F
5,541
Growing degree days, base 45°F
4,287
Growing degree days, base 50°F
3,184
Growing degree days, base 55°F
2,225
Growing degree days, base 60°F
1,409

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,06209
February885010
March734145
April40010156
May17851351
June30145566
July4236697
August7204662
September8389458
October36212177
November668041
December925012

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 9.7 km from Roane County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00468384 (Spencer). Public domain.